CREATE TABLE IF NOT EXISTS scheduled_notifications (
    id BIGSERIAL PRIMARY KEY,

    channel TEXT NOT NULL CHECK (channel IN ('email', 'sms', 'push')),
    title TEXT,
    message TEXT NOT NULL,
    html TEXT,

    scheduled_at TIMESTAMPTZ NOT NULL,

    status TEXT NOT NULL DEFAULT 'pending'
        CHECK (status IN ('pending', 'processing', 'sent', 'failed', 'cancelled')),

    target_user_ids BIGINT[],
    target_role TEXT,
    target_raw JSONB,

    attempt_count INT NOT NULL DEFAULT 0,
    last_error TEXT,
    processing_started_at TIMESTAMPTZ,
    sent_at TIMESTAMPTZ,
    cancelled_at TIMESTAMPTZ,

    created_by BIGINT NOT NULL REFERENCES users(id),
    created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,

    CONSTRAINT scheduled_notifications_target_required CHECK (
        (target_user_ids IS NOT NULL AND array_length(target_user_ids, 1) > 0)
        OR target_role IS NOT NULL
        OR target_raw IS NOT NULL
    )
);

CREATE INDEX IF NOT EXISTS idx_scheduled_notifications_due
ON scheduled_notifications (scheduled_at)
WHERE status = 'pending';

CREATE INDEX IF NOT EXISTS idx_scheduled_notifications_status
ON scheduled_notifications (status, scheduled_at);